As far as possible, the analyses we use are designed to be
agnostic about the causes of variation in a particular variable.
Unfortunately, the same absence of a priori bias is not always
found among our scientific peers! A referee once wrote in a report on
a manuscript describing a twin study:

It is probably alright to use the twin study to estimate the genetic
contribution to variables which you know are genetic like stature and
weight, and it's probably alright for things like blood pressure. But
it certainly can't be used for behavioral traits which we know are
environmental like social attitudes!

Such a crass remark nevertheless serves a useful purpose because it
illustrates an important principle which we should strive to satisfy,
namely to find methods that are trait-independent; that
is, they do not depend for their validity on investigators a
priori beliefs about what causes variation in a particular trait.
Such considerations may give weight to choosing one study design
rather than another, but they cannot be used to decide whether we
should believe our results when we have them.
Next:3 Biometrical Genetical and Up:1 Variation Previous:1 Variation is Everywhere
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Jeff Lessem
2002-03-21